Since Matilda had secretly transferred her property to the Church before her marriage, Welf left her in 1095 and, together with his father, changed sides to King Henry IV, possibly in exchange for a promise of succeeding his father as duke of Bavaria.

After his father's death in 1101 Welf indeed inherited the office of duke of Bavaria. He continued his alliance with the kings; he did not remarry and died childless in 1120. Welf was buried at Weingarten Abbey.